The present invention relates generally to methods for treating plants that increase the resistance or tolerance of a plant to the effects of plant stress and/or stimulate plant growth.
Biological stress has been defined as xe2x80x9cany change in environmental conditions that might reduce or adversely change a plant""s growth or developmentxe2x80x9d (J. Levitt, 1972, Responses of Plants to Environment Stresses, Academic Press, Inc., New York and London). Adverse environmental conditions such as water deprivation, pathogen attack, salinity and unfavorable growing temperatures are common stresses that limit agriculture yields. For example, it has been estimated that the world rice production would decrease 50% if the world mean temperature dropped by only 1.0xc2x0 C. (F. B. Salisbury and C. W. Ross, Stress Physiology in Plant Physiology, 1985, published by Wadsworth Inc.). Moreover, a comparison of average and record yields of eight major crops showed that average yields were only one-third to one-seventh of record yields (Boyer, Science, 1982, 218:443-448). More than 70% of the loss of potential yields was attributed to unfavorable growing conditions caused by factors such as weeds, disease, soil, climate, etc. (Id.).
Unlike animals, which are able to move into less stressful environments, plants rely on chemical defenses to respond to stress. When plants are exposed to unfavorable high growing temperatures, normal protein synthesis is reduced and rapid synthesis of heat shock proteins commences (J. L. Key and Y. M. Chem 1981, Proc. Natl. Acad. Science 78:3526-3530). Similarly, low temperature acclimation in plants is associated with the synthesis of specific, extremely hydrophilic proteins which act as cryoprotectants, much like anti-freeze (J. G. Boothe et al., 1997, Plant Physiol. 113:367-376). In response to invasion of plant tissues by pathogens such as insects or fungi, stress-induced lignin deposition occurs to seal off the site of wounding (R. A. Dixon and N. L. Pawa, 1995, Plant Cell 7:1085-1097). Many plants respond to drought and salinity stress by accumulating high levels of protein, which is believed to protect plant tissues from osmotic stress (G. R. Stervant, et al., 1976, Plant 120, 279-289).
Even though plants have developed specific patterns of stress-mediated metabolism in response to various environmental and biological challenges, adverse environmental conditions still limit agriculture yields. Efforts to mitigate or increase the resistance of a plant to the effects of plant stress have included complex methodologies that are both time-consuming and expensive. For example, in order to inhibit pathogenic conditions of plants, recombinant DNA technology has been used to incorporate genes into the plant genome that encode polypeptide and complementary oligonucleotide inhibitors. Such a method, directed at mitigating the effects of pathogen stress, would not be expected to mitigate, or increase the resistance of a plant to, the effects of different forms of stress. For example, such a method would not be expected to protect plants from heat or cold stress. Therefore, it is usually necessary to incorporate other genes into the plant""s genome that will be effective in eliminating the particular stress involved. A simple, safe and cost-effective method to increase the resistance of a plant to the effects of a wide variety of plant stresses is needed. The present invention addresses this need.
It has been discovered that application of glycolic acid to plants increases the resistance of the plants to the effects of plant stress. Accordingly, the present invention provides methods for increasing the resistance of plants to the effects of plant stress utilizing glycolic acid.
In one aspect of the invention, a method of increasing the resistance of a plant to the effects of plant stress includes treating the plant with glycolic acid, a salt thereof, or a mixture thereof. The plant is typically treated with an amount of glycolic acid effective in increasing the resistance of the plant to the effects of plant stress. The method preferably includes treating the plant with the aforementioned compounds or compositions prior to the occurrence of plant stress. In one embodiment, the salt of glycolic acid is an ammonium salt.
In yet another aspect of the present invention, a method of increasing the resistance of a plant to the effects of plant stress includes predicting when a stressful condition will arrive and then treating the plant with glycolic acid, a salt thereof, or a mixture thereof, prior to the occurrence of plant stress.
It has also unexpectedly and surprisingly been discovered that application of an ammonium salt of glycolic acid stimulates plant growth significantly more than glycolic acid. Accordingly, in yet another aspect of the invention, methods of treating plants are provided that include treating the plant with an effective amount of an ammonium salt of glycolic acid.
It is an object of the present invention to provide methods of increasing the resistance of a plant to the effects of plant stress.
It is a further object of the invention to provide methods for treating plants to stimulate plant growth.
These and other objects and advantages of the present invention will be apparent from the following description.